CVE-2020-14929: 
NixOS vulnerability analysis and mitigation

Alpine email client versions before 2.23 contain a security vulnerability (CVE-2020-14929) where the application silently proceeds to use an insecure connection after a /tls command is sent in certain circumstances involving PREAUTH. This behavior is considered less secure than the alternative of closing the connection and allowing the user to make an informed decision about how to proceed (Debian LTS, MITRE CVE).

The vulnerability affects the STARTTLS implementation in Alpine's email client, specifically in scenarios involving PREAUTH (Pre-Authentication) mechanisms. When encountering certain conditions during the TLS negotiation process, the client fails to properly handle the security downgrade, potentially exposing users to insecure communications (Record Media).

The vulnerability could lead to exposure of sensitive information as the client continues communication over an insecure channel without properly alerting the user. This creates a potential risk for man-in-the-middle attacks where an attacker could intercept or manipulate email communications (Debian Security Tracker).

The vulnerability requires an attacker to be in a position to intercept the STARTTLS negotiation process. While no active exploits have been reported in the wild, the vulnerability is particularly concerning in scenarios where network communications can be intercepted (Record Media).

The vulnerability has been fixed in Alpine version 2.23. Users are advised to upgrade to this version or later. Multiple distributions have released security updates, including Debian with version 2.11+dfsg1-3+deb8u1 for Jessie, and Fedora with version 2.23-2 for both Fedora 31 and 32 (Fedora Update, Debian LTS).